em wrote:You cant do just one chain and leave it at that - they require a proof by contradiction, don't they?

MCC wrote:They do.

yes, when i find myself forced to use a proof-by-contradiction, i do always insist on developing both branches

yet reading the discussions on Deducing From Uniqueness, you could conclude that the extra Given (i.e. we are given that the puzzle has only one answer) permits ignoring the 2nd branch whenever the 1st branch did happen to produce an answer!

MCC - I accept your amendment, and I think its covered by the without a logical reason bit. You were guessing if you accept the answer and the puzzles solved. If it doesnt work and you test another candidate, are youre back into T & E because now you have a logical reason for choosing the next candidate? Yes, I think so, but its a fine line, all right.

Pats comment that uniqueness can remove the need for trialling should also be covered by without a logical reason.

I'm still on the trail of the puzzle anywhere that disproves the point that a puzzle requiring a guess may have only one solution. At the beginning of this thread simes challenged this statement

em wrote:You can guess if you want but if you need to guess then it means that the puzzle has multiple solutions and is invalid.

then he went off and never came back. So I'm just looking for someone else to fight with over it. (Pat? )

i finished my deeds! ...and i got today's newspaper sudoku daily puzzle... and guess what? i was about to finish it, without guessing, on account that none was needed... and with four empty cells, the for gave as candidates: 4 & 6... (see puzzle below, row four & 6,... second and last cells of both... )

i did not want to guess so i typed the puzzle, worked it in simple sudoku and got to the same "guessing point"...

no other way... i took my plunge and hit the 4 on cell r4c2 (row 4 column 2)... and it was accepted!... and finished filling the puzzle no guess needed. But went back with undo and tried again, this time I hit the 6 on cell r4c2 (row 4 column 2)... and it fished ok, with no errors, according to simple sudoku softwre so? Seems to me there are puzzles with two accepted solutions. Which means the puzzle has the solution that possibilities or candidates might indicate as acceptable!

em wrote: You can guess if you want but if you need to guess then it means that the puzzle has multiple solutions and is invalid.

then he went off and never came back. So I'm just looking for someone else to fight with over it. (Pat? :D)[/quote]

Im just humbly collaborating now, maybe Im wrong assuming my discovery is not what you mentioned? I had decided not coming back to the forum but what the heck, I thought it is far more relevant that what I had been asking: is there only one solution? got answered with this maybe accidental excemption to the rule?...

Hi Gongora. What a surprise! Perhaps I wasn't clear - there are a lot of puzzles out there that have multiple solutions. They are invalid but they're still published. You need to check the source - they should tell you that there is more than one solution. Pappocom puzzles only ever have one solution.

When you put your puzzle into SS it should tell you on the bottom line that the puzzle is invalid.

chicago suntimes has had puzzles with many solutionsgota watch out for thosebut in the end, you still need to guess and see if the guess will work or notthere is many games where there is no choice but to guess

em says: "Pappocom puzzles only ever have one solution..."...maybe the chicago newspaper, the one with invalid puzzles is the same group that syndicates sudoku puzzles from same source as our La Nación Costa Rica newspaper... and this invalid one i copied from todays issue... and i read that all newspapers get their puzzles from Pappocom... so i am lost!

to be honest, i just into to this gameso alot of this lingo is new to meall i know is that the chicago tribune is what got me startedand i do remember on puzzle, i had the option for two different valid solutionsas far as what is pappocom i have no idea

on side note, i do get stuck on alot of sudoku games and have to resort guessing on a 50-50 squares and see if the solution from that guess is valid

if this section still has correspondents... i just wanted to report a "simple sudoku" puzzle that, when trying a 50/50 candidate, accepts either without warning that one is an impossible choice... it will lead to a no solution possible!

Umm .. MCC, its the edit button not the quote button. I hate to keep on correcting you, it makes me sound like a know-all and Im not on your case or anything either, I just keep stumbling across you. Honest!

Gongora, the edit button pops up when you log in. If you edit before anyone else replies, you get away with it. If not, then Wayne writes a message in little letters underneath to say that the post was edited.

MCC is right - start a new post every time so that we keep to one thread/one idea, but just to finish this one off - Simple Sudoku will not accept an incorrect clue if you 'block invalid moves' otherwise it accepts anything (within reason).

...for instance: where is the "edit" button? ...i always start writing after i hit "quote" and erase whatever comes...

I just read: "Gongora, the edit button pops up when you log in. If you edit before anyone else replies, you get away with it. If not, then Wayne writes a message in little letters underneath to say that the post was edited...

question: what means edited by wayne? is it a prerequisite? i'll tell you what. 'am gonna close now, sign out and log in... and will loof for the misterious edit button! but first...

i will start a new post every time so that we keep to one thread/one idea...

...just to finish this one off - Simple Sudoku will not accept an incorrect clue if you 'block invalid moves' otherwise it accepts anything (within reason)... you see? great help! i went to options and found the option! THANKS! ...will be back! chau...

Until reading this thread I has equated Trial and Error with guessing. I have now changed my opinion.

Trial and Error is a logical deduction technique that removes a posibility by finding that it always leads to a contridiction. A trial that happens to find a solution is a guess and you have not completed the puzzle*.

(*unless you also include the uniquness principle that if you find 1 solution to a valid Sudoku you have found them all)